1. Field of the Invention
The present invention relates to a recording material such as a thermal recording material and a pressure-sensitive recording material, which includes a diazo compound, a coupler compound that can react with the diazo compound to form a color, and a metal salt. Specifically, the present invention relates to a recording material that can form a vivid color image ranging from violet to cyan hues.
2. Description of the Related Art
With the development of High-performance recording materials such as high-performance thermal or pressure-sensitive recording materials, there has been a great demand for a thermal recording material that can form a vivid color image ranging from violet to cyan hues and also has excellent in shelf life and image storage stability (image storability).
Diazo compounds react with the so-called coupler compounds such as phenol derivatives and active methylene group-containing compounds to form azo dyes. The diazo compounds are also decomposed by light radiation and thus lose their activity. Based on such properties, the diazo compounds have been utilized since early times as optical recording materials typified by diazo copying materials. For example, such applications are disclosed in “Fundamentals of Photographic Engineering, Edition of Non-Silver Salt Photography” edited by the Japan Photographic Association, published by CORONA PUBLISHING, Ltd., 1982, pp. 89–117 and 182–201.
Lately, the diazo compounds have also been applied to recording materials for processes involving image fixing. Typical examples of such recording materials include light-fixation type thermal recording materials, which comprise a diazo compound and a coupler compound. In such materials, the diazo compound and the coupler compound are heated in response to image signals to react with each other, so that images are formed, and then the images are fixed by light radiation. For example, such materials are described in Kohji Sato et al., J. Image Electronic Society, Vol. 11, No. 4, 1982, pp. 290–296.
Even in dark places, however, diazo compounds in such recording materials gradually thermally decompose and thus lose their reactivity. Therefore, such recording materials have the disadvantage of having a short shelf life. In order to overcome such a disadvantage, diazo compounds may be encapsulated in microcapsules so as to be separated from decomposition-causing materials such as water and bases. Such a technique is disclosed in Toshimasa Usami et al., J. Electrophotography Association, Vol. 26, No. 2, 1987, pp. 115–125. Such a technique can dramatically improve the shelf life of the recording material.
Further, the microcapsule has a glass transition temperature higher than room temperature, the wall of the capsule is non-permeable to substances at room temperature. Furthermore, such a microcapsule is permeable to substances at a temperature higher than the glass transition temperature. For this reason such a microcapsule can be thermally responsive and can therefore be used for a thermal recording material. Specifically, a thermal recording material can be produced by forming, on a support, a thermal recording layer that includes diazo compound-containing thermally responsive microcapsules, a coupler compound and the like. Such a thermal recording material can (1) provide long storage stability for the diazo compound, (2) form thermal coloring images, and (3) provide image fixation by light radiation.
In recent years, attempts have been made to develop recording materials that can perform sophisticated functions. Functional materials have become widespread, such as recording materials that can form multi-color images, as disclosed in Japanese Patent Applications Laid-Open (JP-A) Nos. 4-135787 and 4-144784. Under such circumstances, there have been demands for further improvements in performance, particularly demands for good coloring hues for images and demands for improvement in the resistance of image portions to light.